Methods and apparatus for delivering peritoneal dialysis (pd) solution with a peristaltic pump

ABSTRACT

In one aspect, the invention provides methods and apparatus for delivering peritoneal dialysis (PD) solution (or other fluids), from a supply to a patient. A first pump, in fluid coupling with the supply, delivers PD solution from the supply to a “mesne” (or intermediate) measuring element, and generates signals indicative of a volume of that delivered PD solution. The mesne measuring element, in fluid coupling with the first pump, generates signals indicative of a volume of PD solution received from that pump. A second pump, fluidly coupled to the mesne measuring element, routes PD solution from the mesne measuring element for delivery to the patient.

BACKGROUND OF THE INVENTION

The invention relates to apparatus and methods for delivering fluids toa patient and, more particularly, to apparatus and methods forperitoneal dialysis (PD). It has application, inter alia, in thedelivery of PD solution to a patient, for example, during automatedperitoneal dialysis (APD) procedures.

Peritoneal dialysis (PD) is a medical procedure for removing toxins fromthe blood that takes advantage of the semi-permeable membranesurrounding the walls of the abdomen or peritoneal cavity. During a PDprocedure, a solution is introduced into the patient's abdomen, where itremains for up to several hours, removing blood toxins via osmotictransfer through that membrane. At completion of the procedure, thesolution is drained from the body along with the toxins. In APD, theentire procedure is handled by automated equipment.

There are many systems on the market today for performing APD.Typically, such systems include a pumps and a variety of other complexcomponents. In today's economy, cost is an ever-increasing issue, and PDequipment manufacturers have attempted to reduce production costs byseveral means. One is to employ peristaltic pumps, which can beinexpensive, though, they have inherent limitations. For example,accurately measuring the fluid volume delivered by a peristaltic pumpcan be difficult, e.g., because the tubing in the pump loses elasticityand, consequently, its volume changes over time. PD pumps also tend todevelop pinhole leaks in pump tubing.

An object of the invention is to provide improved methods and apparatusfor delivering fluid to a patient.

A further object of the invention is to provide such improved methodsand apparatus for delivering PD solutions to a patient.

A still further object is to provide such improved methods and apparatusas can be adapted for using conventional pump technologies, e.g.,peristaltic pumps.

A still further object of the invention is to provide such methods andapparatus as can be implemented at reasonable cost, yet, produceefficacious results.

SUMMARY OF THE INVENTION

In one aspect, the invention provides methods and apparatus fordelivering peritoneal dialysis (PD) solution (or other fluids), from asupply to a patient. A first pump, in fluid coupling with the supply,delivers PD solution from the supply to a “mesne” (or intermediate)measuring element, and generates signals indicative of a volume of thatdelivered PD solution. The mesne measuring element, in fluid couplingwith the first pump, generates signals indicative of a volume of PDsolution received from that pump. A second pump, fluidly coupled to themesne measuring element, routes PD solution from the mesne measuringelement for delivery to the patient.

In related aspects, the invention provides methods and apparatus fordelivering peritoneal dialysis (PD) solution as described above furthercomprising one or more digital data processors in communicationscoupling with any of the first pump and the mesne measuring element,wherein the one or more digital data processors provide forredundancy-based determination a volume of PD solution delivered to thepatient in response to the signals generated by the first pump and/orthe mesne measuring element.

In further related aspects, the invention provides methods and apparatusfor delivering peritoneal dialysis (PD) solution as described above inwhich the second pump comprises a peristaltic pump. The peristaltic pumpcan route the PD solution directly to the patient or it may route itthrough an intermediary apparatus.

In still further related aspects, the invention provides methods andapparatus for delivering peritoneal dialysis (PD) solution as describedabove wherein the first pump includes a chamber in which the volume ofdelivered PD solution is determined, e.g., by one or more digital dataprocessors responsive to signals generated by the first pump.

In other related aspects, the invention provides methods and apparatusfor delivering peritoneal dialysis (PD) solution as described above inwhich the first pump comprises a piezoelectric (“piezo”) pump. The piezopump can, according to further related aspects of the invention,comprise a plurality of piezoelectric elements, e.g., piezo “strips,”wherein at least one of those elements comprises a piezoelectric sensor,e.g., a piezo sensor strip. That strip can, according to related aspectsof the invention, generate the volume-indicative signals discussedabove.

The invention provides, in other related aspects, methods and apparatusfor delivering peritoneal dialysis (PD) solution as described above inwhich signals generated by the first pump, e.g., the piezo pump, areproportional to the volume of delivered PD solution. In further relatedaspects, those signals are proportional to a volume of PD solution inthe aforesaid chamber.

In related aspects, the invention provides methods and apparatus fordelivering peritoneal dialysis (PD) solution as described above in whichthe first pump comprises a plurality of pumps, e.g., piezo pumps, eachin fluid coupling with the supply, that deliver PD solution from it tothe mesne measuring element. As above, one or more of those pumps cangenerate signals indicative of a volume of that delivered PD solution.These signals can represent, for example, time and/or voltage associatedwith activation of the piezo pumps.

In further related aspects, the invention provides methods and apparatusfor delivering peritoneal dialysis (PD) solution as described above inwhich the first pump, e.g., the piezo pump (or pumps), generate(s)signals indicative of a volume of solution according to a duration oftime empty the chamber (e.g., during the course delivering solution tothe mesne measuring element).

In related aspects, the invention provides methods and apparatus fordelivering peritoneal dialysis (PD) solution as described above in whichthe first pump delivers solution to the mesne measuring element atlow-pressure and/or against a constant pressure head height.

In further related aspects, the invention provides methods and apparatusfor delivering peritoneal dialysis (PD) solution as described above inwhich the mesne measuring element generates a volume-indicative signal(e.g., electrical, optical, etc.) based on a height of received PDsolution in the chamber.

In related aspects, the invention provides methods and apparatus fordelivering peritoneal dialysis (PD) solution as described above in whichthe mesne measuring element delivers the received PD solution to thesecond pump, e.g., via gravity-assist. In further related aspects, theinvention provides methods and apparatus for delivering peritonealdialysis (PD) solution as described above in which the second pump pullsthe PD solution from the mesne measuring element for routing of the PDsolution for delivery to the patient.

In related aspects, the invention provides methods and apparatus fordelivering peritoneal dialysis (PD) solution as described above in whichthe first pump and the mesne measuring element are disposed within aremovable and/or disposable cassette.

Further aspects of the invention are evident in the drawings and in thedescription that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be attained byreference to the drawings, in which:

FIG. 1A depicts a system for delivering peritoneal dialysis (PD)solution from a supply to a patient according to one practice of theinvention and of the type with which the invention can be practiced;

FIG. 1B depicts further details of the pumps and mesne measuring elementof the system of claim 1; and

FIG. 2 depicts a more detailed view of bimorph-based pumps of the systemillustrated in FIGS. 1A-1B.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

FIG. 1A depicts a peritoneal dialysis (PD) system 10 for delivering PDsolution (or other fluid) to a patient according to one practice of theinvention. The system 10 includes a supply bag 20 with fresh PD solution25, a drainage bag 30, pumps 40 and 50, heater 60, solution chamber 71,pump 80, and pressure sensor 100. These elements are fluidly coupled(i.e., coupled for fluid flow) to one another, and with the patient, asindicated by the lines connecting them in the drawing and/or asdiscussed below. The system 10 facilitates inter alia introducing freshPD solution into, and removing spent PD solution from, the peritoneum110 of a patient 120.

In some embodiments, one or more components 40-100 are embodied within aremovable cassette 15 which can be inserted into a suitably designedrecess or receptacle of a dialysis machine or other apparatus (notshown) for delivering and/or routing PD solution (or other fluid) inaccord with the teachings hereof. The cassette 15 comprises a basestructure made of plastic, or other suitably rigid material, and can beconstructed and operated as generally described, by way of non-limitingexample, in commonly assigned U.S. Pat. No. 6,743,201, filed Apr. 1,1999, entitled “Cassette for Delivering Fluids, Especially DialysisFluids” (the teachings of which are incorporated herein by reference),all as adapted in accord with the teachings hereof. Fluid couplingbetween the components 40-100 in these embodiments is provided by tubingor vias (ducts) intergral to and/or otherwise provided with the cassette15, in the conventional manner known in the art as adapted in accordwith the teachings hereof. Fluid coupling to the patient is provided viacatheters and ports, and that with supply and drainage bags 20, 30 isprovided via tubing—again, in the conventional manner known in the art.

In other embodiments, the components 40-100 may comprise functionalityintegral to and/or disposed within a dialysis machine (or other fluiddelivery system) and/or they may comprise individual (or “stand-alone”)elements which can be used, e.g., as part of a kit and/or within avariety of fluid delivery systems. As above, fluid coupling between thecomponents in these embodiments is provided by tubing or vias (e.g., inthe case of components integral to dialysis machines or otherequipment), while coupling to the patient is provided via catheters andports, and that with supply and drainage bags 20, 30, via tubing—all inthe conventional manner known in the art as adapted in accord with theteachings hereof.

The supply bag 20 holds fresh PD solution 25 (or other fluid) fordelivery to the patient 120 (or, more particularly, to the peritoneum110, which detail will be assumed for the remainder of the discussion)and, in the illustrated embodiment, comprises a conventional PD solutionsupply bag of the type known in the art (e.g., a PVC plastic bagcontaining one to several liters of PD solution). The drainage bag 30holds spent PD solution that has been drained from the peritoneum 110 ofthe patient 120 (e.g., via gravity-assist, pump 80 or otherwise), and,in the illustrated embodiment, comprises a conventional container of thetype known in the art for this purpose (e.g., a PVC bag or otherwise).

The pumps 40 and 50 deliver PD solution (or other fluid) from the supply20 to the solution chamber 71, a component of the mesne (i.e.,“intermediate”) measuring element 70 (see FIG. 2 and discussion below),and additionally facilitate measuring a volume of that delivered PDsolution, as discussed further below. In the illustrated embodiment, thepumps 40 and 50 comprise piezoelectric pumps, though, in otherembodiments they may comprise other types of pumps or apparatus fordelivering and/or measuring fluids in accord with the teachings hereof.Although there are two pumps in the illustrated embodiment, otherembodiments may include a greater or lesser number (piezoelectric orotherwise).

The heater 60 brings fresh PD solution to an appropriate temperature(e.g., 37° C.) for delivery to the patient 120. In the illustratedembodiment, the heater 60 comprises a heating element disposed in oraround a fluid flow-line of cassette 15 that heats the PD solution as itpasses from supply 20 to pumps 40 and 50. In other embodiments, theheater 60 is disposed in or around supply 20, pumps 40-50 and/or otherelements of the illustrated system 10 upstream of patient 120. Examplesof suitable heating elements include in-line heaters that providethermo-acoustic heating, e.g., as maintained by processor or fuzzy logic150 (hereinafter, “processor 150”). Indeed, in some embodiments, thecooling “side” of such heaters can be used to cool electronics and othercomponents of the system 10, thereby, enabling a reduction in overallsystem size.

The solution chamber 71 holds and facilitates measuring a continuousflowing volume of PD solution (or other fluid) received from pumps 40and 50 and passed to pump 80. The chamber 71 is sized for use withoptical elements 72, 73 and, more generally, to afford measurement ofcontinuous volumes or “batches” of the solution, e.g., in the mannerdiscussed below. In the illustrated embodiment, the solution chamber 71comprises a 40 mL chamber, though in other embodiments it may be sizedotherwise, e.g., from 1-100 mL, 25-75 mL, or otherwise.

The chamber is preferably optically clear (or at least partially so) towavelengths used to measure volumes of solution in it (again, asdiscussed below). For embodiments in which it forms part of a cassette15, the chamber 71 comprises a cavity having walls of plastic (or othermaterial) with apertures, fittings and/or otherwise shaped toaccommodate elements 72, 73 and to allow light rays (e.g., visible,ultraviolet, infrared or otherwise) generated and received by them topass with minimal attenuation therebetween. For cassette-lessembodiments, element 71 can comprise a flow-chamber defined by like suchwalls integral to the fluid flow-path within a dialysis machine (orother fluid delivery system) and/or by a stand-alone vessel withsuitable inlets and outlets. Although only one solution chamber 71 isshown in the drawing, other embodiments may include additional suchchambers.

The pump 80 routes PD solution (or other fluid) received from thesolution chamber 71 for delivery to the patient 120, either directly(e.g., via appropriate catheters and ports) or via additional apparatus(not shown) such as filtration equipment, additional heaters, monitoringapparatus, etc. In the illustrated embodiment, pump 80 comprises aperistaltic pump of the type known in the art, as adapted in accord withthe teachings hereof, e.g., with flexible tubing or other structuressuitable for defining an arc-like (or other) fluid-flow path that can becompressed by rollers (not shown), or the like, in a continuous rhythmicfashion to effect peristalsis—and, more particularly, to peristalticallypull fluid from chamber 71 and/or deliver it to patient 120 (again,directly or indirectly).

For embodiments utilizing a cassette 15, flexible tubing or otherstructures defining the compressible fluid-flow path of pump 80 can beembodied in and/or integral to the cassette, Moreover, the pump 80 cancomprise an aperture and/or recess in cassette 15 adapted to receive oneor more peristaltic pump rotors (with rollers) integral to the dialysismachine in which the cassette is inserted. For cassette-lessembodiments, pump 80 can comprise a peristaltic pump defined by liketubing, rotors, etc., integral to a dialysis machine (or other fluiddelivery system) and/or by a stand-alone vessel with suitable inlets andoutlets. Although only one pump 80 is shown in the drawing, otherembodiments may include additional such pumps (peristaltic or otherwise)instead of, or in addition to, the single pump 80 shown here.

The pressure sensor 100 facilitates measuring a pressure at which thepump 80 expels solution for delivery to the patient 120. The sensorcomprises a conventional pressure sensor of the type known in the artand suitable for such purpose. In the illustrated embodiment, it iscoupled to the output of the pump 80 via pressure line 90. The pressuresensor 100 generates an analog or digital output indicative of thesensed pressure for transmission to processor 150, which monitors (andlogs) the pressure values to maintain, or otherwise manage, a pressureflow of the pump 80. In this regard, processor 150 can control the pump80 speed in order to maintain the fluid pressure at the output of pump80 within a predetermined range (e.g., between 1.0 and 2.0pounds-per-square-inch or a pressure suitable neonatal solutiondelivery, etc.).

FIG. 1B is a more detailed view of the PD system 10 of FIG. 1. Thesystem 10 includes, inter alia, pumps 40 and 50, solution chamber 71 andpump 80, as discussed above. The text that follows further discussesthese components and the remaining components of the mesne measuringelement 70, namely, an illumination source 72, a lens system 73 and animage capture medium 74. Those skilled in the art will appreciate thatother embodiments may include a greater or lesser number of suchcomponents, instead of, or in addition to, the components discussedbelow.

Generally, as discussed above, the pumps 40 and 50 deliver PD solution(or other fluid) from the supply 20 to the solution chamber 71 andadditionally facilitate measuring a volume of that delivered PDsolution. In the illustrated embodiment, the pumps 40 and 50 comprisepiezo pumps that pump against a constant pressure head-height of thesolution chamber 71 to effect delivery of the PD solution, although thisis not a requirement of the system 10.

Referring to FIG. 2, more particularly, pump 40 comprises a chamber 40 aand a bimorph 45. In the illustrated embodiment, the bimorph 45 servesas a piston to draw PD solution (or other fluid) into and expel it fromthe pump chamber 40 a (for routing to solution chamber 71). The chamber40 a is sized to accommodate the bimorph 45 and, in the illustratedembodiment, comprises a 20 mL chamber, though in other embodiments itmay be sized otherwise, e.g., from 1 mL-100 mL, 25-75 mL, or otherwise.

The chamber 40 a includes at least one inlet for receiving fluids, e.g.,governed by valve 46, and at least one outlet for delivering fluids,e.g., governed by valve 47. For embodiments in which it forms part of acassette 15, the chamber 40 a comprises a cavity having at least oneelastomeric or other flexible side-wall of latex, vinyl, and/or nitrilefilm (or other suitable material) against which bimorph 45 flexes andflattens, thereby, “pistoning” fluid into and out of the chamber 40 a.In such an embodiment, the bimorph 45 is disposed outside the pumpchamber 40 a, in adhesive contact with the film. For cassette-lessembodiments, element 40 a can comprise a chamber having like flexibleside wall(s) integral to a dialysis machine (or other fluid deliverysystem) and/or by a stand-alone vessel with such side wall(s). In thesecassette-less embodiments, the bimorph 45 can be integral to the wall,e.g., without intervening elastomeric film.

In the illustrated embodiment, the bimorph 45 comprises a stack of oneor more piezo strips or elements 45 a-45 c that alternatively flex andflatten, as driven by sinusoidally (or other) varying signals applied bya voltage source 81, thereby drawing fluid into and expelling it out ofthe chamber 40 a. In this regard, action of the bimorph 45 isfacilitated by valves 46, 47, positioned at the intake and exit of thechamber 40 a, as illustrated, which can comprise piezoelectric valvesdriven (e.g., by voltage source 81 or otherwise) to open and close insynchronism with bimorph 45, although, in other embodiments they maycomprise one-way mechanical valves, or the like. Such piezo valves caninclude feedback elements of the type described below that signalopening and closing of the valves, e.g., for use by processor 150 incontrolling and/or logging system operation. Voltage source 81 of theillustrated embodiment is controlled by processor 150, e.g., to supplyPD solution to chamber 71 at a rate coordinated with pump 80.

Illustrated bimorph 45 comprises three strips: two outer strips 45 a, 45c that flex (in opposite directions) under an applied voltage, and oneinner strip that generates an electrical signal (e.g., voltage orcurrent) in response to flexing. The outer strips 45 a, 45 c arereferred to as “actuator” strips. The inner strip 45 b is referred to asa “sensor” or “feedback” strip. In the illustrated embodiment, eachstrip is sized sufficient to pump PD solution (or other fluid) at a lowpressure (e.g., between 1.0 psi and 2.0 psi), and are sandwichedtogether via adhesive, ultrasonic welding, and so forth. Preferredmaterials for the strips 45 are polymers (e.g., polyvinylchloride and/orpolyvinylflouride) or ceramics (e.g., lead zirconate titanate). Otherembodiments may be constructed otherwise (e.g., fewer piezo strips, nofeedback strip, additional feedback and/or sensing strips, varyingmaterials, etc.).

As discussed above, the piezoelectric pump 40 also facilitates measuringa volume of PD solution in the chamber 40 a. The illustrated feedbackpiezo strip 45 b generates an electrical signal indicative of its degreeand direction of bending, e.g., varying from a peak negative voltage orcurrent when maximally flexed in one direction to a peak positivevoltage or current when flexed maximally in the other direction. Thatelectrical signal is transmitted to processor 150, which determines thevolume of solution pumped in each cycle of element 40 as a function ofthe peak-to-peak timing and voltage.

More particularly, pump 40 and processor 150 are calibrated (e.g., atthe manufacturing plant, upon insertion of cassette 15, at start oftreatment or otherwise) by recording that peak-to-peak timing andvoltage during movement of the bimorph 45 across an empty chamber 40 a.Preferably, this is repeated several times in order to increase accuracyof the calibration. In operation, data processor 150 compares thecalibration-phase peak-to-peak timings and voltages with thosetransmitted by the strip 45 b while pumping PD fluid into and out ofthat same chamber 40 a. The data processor then determines the volume ofsolution pumped in each cycle as a function of the difference in thosetimings and voltages, the volume of the chamber, the viscosity andspecific gravity of the fluid. The processor also sums the per-cyclevolumes to determined the overall volume delivered to chamber 71. Theprocessor 150 monitors (and logs) values of those volumes to maintain,or otherwise manage, the pump 40—e.g., to control a rate which itsupplies PD solution to chamber 71 and to control the amount of fluiddelivered to it (and, ultimately, the patient).

Illustrated pump 50 (including, chamber 50 a, bimorph 55, valves 56, 57)are constructed and operated similarly to pump 40 (and its constituentcomponents), though, in other embodiments, pumps 40, 50 may be operatedin other and/or dissimilar ways.

Referring back to FIG. 1B, the mesne measuring element 70 facilitatesmeasuring a volume of PD solution (or other fluid) in the chamber 71. Itincludes, in addition to the solution chamber 71, an illumination source72, lens system 73 and an image capture device 74. The illustratedillumination source 72 emits a pattern of light rays (e.g., visible,ultraviolet, infrared or otherwise) that are aimed to pass through thechamber 71, preferably, coherently (e.g., via laser “light”). Indeed, insome embodiments, the illumination source 72 generates these rays at twoor more frequencies. Regardless, the wavelength(s) are selected forminimum attenuation in air and maximum attenuation in PD solution (orother delivered fluid). Accordingly, rays that pass through the filled,bottom region of the chamber are attenuated, while those that passthrough the empty, top region are not. In the illustrated embodiment,the illumination source 72 comprises one or more laser diodes or laserdiode arrays of the type commercially available in the marketplace, asadapted in accord with the teachings hereof. These can be arranged toemit a bar or grid pattern of rays that extends from the bottom to thetop of the chamber 71. It will be appreciated that the rays emitted bysource 72 may be formed into a pattern in other ways, as well, e.g., byetchings on walls of the chamber 71, and so forth.

The illustrated lens system 73 focuses and projects the rays that havepassed through the chamber onto image capture device 74 to facilitatedetection of a height (and, therefore, a volume) of solution in thechamber 71. Illustrated lens system 73 comprises one or moreconventional lenses and/or prisms of the type commercially available inthe marketplace suitable for such purpose, as adapted in accord with theteachings hereof.

Image capture device 74 captures the pattern of attenuated andunattenuated rays focussed thereon by the lens system 73. In theillustrated embodiment, the device 74 comprises a charge-coupled-device(CCD) array of 640×480 pixels, although in other embodiments it maycomprise a smaller or larger array (e.g., a one-dimensional array, alower-resolution array, etc.), and/or use different types of medium(e.g., CMOS sensors, etc). For higher resolution, larger arrays can beused. Typical pixel sizes for the arrays can range from 6.8 to 24microns, though sizes on the smaller end of this range are preferable inorder to improve accuracy. The illustrated CCD array 74 operates in theconventional manner known in the art of digital imaging, albeit asadapted in accord with the teachings hereof.

Processor 150 determines a volume of solution in the chamber 71 as afunction of the pattern of rays captured by device 74. It does thisperiodically, e.g., over intervals that substantially the cycle time ofpumps 40, 50. To this end, in the illustrated embodiment, by way ofexample, the processor 150 compares the captured pattern with onesimilarly generated during calibration phase—when the chamber 71 isempty. The comparison is performed using conventional image processingfunctions and the per-period volume determined as a function of thedifferences in the compared patterns. The processor 150 also sums theper-period volumes to determined the overall volume received at chamber71. The processor 150 monitors (and logs) values of those volumes tomaintain, or otherwise manage, coordinated operation of pumps 40/50 and80, e.g., to control a rate which device 10 supplies PD solution to thepatient.

Operation

In operation, by way of non-limiting example, the bags 20 and 30 areconnected as shown in FIG. 1A-B, e.g., by a patient, medical assistantor otherwise. The solution is brought to temperature (e.g., 37° C.) byheater 60, and the processor 150 operates pumps 40, 50, drawing heatedsolution from the supply 20 to the chamber 71. Concurrently, theprocessor 150 determines a volume of that solution, all as describedabove.

Pump 80 delivers solution from chamber 71 to the patient (directly orindirectly), as described above, under control of processor 50. Thevolume of that solution is determined by the processor 150 based on theheight of the solution in chamber 71 as detected by mesne measuringelement 70, also as described above. The processor 150 compares theaforementioned volume determinations to determine—redundantly—how muchsolution has been delivered to the patient.

At conclusion of the treatment cycle, processor 150 opens a valve 82downstream of pump 80 and simultaneously closes other valves (e.g.,valves 46-49) to pump fluid expelled from the peritoneum 110 to drainagebag 30. In the illustrated embodiment, PD solution is drained viagravity-assist, although in other embodiments it may be pumped out(e.g., via pump 80 or otherwise).

Described and shown herein are apparatus and methods for delivering PDsolution to a patient meeting the objectives set forth above. It will beappreciated that the embodiments described here are merely examples ofthe invention and that other embodiments, incorporating changes therein,fall within the scope of the invention. Thus, by way of non-limitingexample, although the illustrated embodiment is directed to an apparatusfor delivering PD solution to a patient, in other embodiments theinvention may be utilized in the delivery of other solutions and fluids.And, by way of further non-limiting example, although cassette 15 may bereplaced by multiple cassettes, each with a respective portion of thefunctionality of cassette 15.

1. An apparatus for delivering peritoneal dialysis (PD) solution from asupply to a patient, comprising A. a first pump, in fluid coupling witha supply of PD solution, that delivers PD solution from the supply to amesne measuring element, the first pump generating signals indicative ofa volume of that delivered PD solution, B. the mesne measuring element,in fluid coupling with the first pump, generating signals indicative ofa volume of PD solution received from the first pump, and C. a secondpump, fluidly coupled to the mesne measuring element, that routes PDsolution from the mesne measuring element for delivery to the patient.2. The apparatus of claim 1 further comprising one or more processors incommunications coupling with any of the first pump and the mesnemeasuring element, wherein the one or more processors determine a volumeof PD solution as a function of the volume-indicative signals generatedby any of the first pump and the mesne measuring element.
 3. Theapparatus of claim 1, wherein the second pump comprises a peristalticpump.
 4. The apparatus of claim 3, wherein the first pump comprises apiezoelectric (“piezo”) pump.
 5. The apparatus of claim 4, wherein thepiezo pump comprises a plurality of piezoelectric elements, wherein atleast one of those elements comprises a piezoelectric sensor.
 6. Theapparatus of claim 5, wherein the piezoelectric sensor generates signalsindicative of a volume of PD solution delivered by the piezo pump. 7.The apparatus of claim 1, wherein the signals generated by the firstpump have peak-to-peak amplitudes and/or timings that are a function ofthe volume of PD solution pumped from the chamber.
 8. The apparatus ofclaim 1 comprising a plurality of said first pumps, each in fluidcoupling with the supply, and each that delivers PD solution from thesupply to the mesne measuring element, the plurality of first pumps eachgenerating signals indicative of a volume of PD solution delivered bythat respective pump.
 9. An apparatus for delivering peritoneal dialysis(PD) solution from a supply to a patient, comprising A. a first pump, influid coupling with the supply, that delivers PD solution from thesupply to a mesne measuring element, B. the mesne measuring elementincluding a chamber that is in fluid coupling with the first pump andthat receives PD solution from the first pump, the mesne measuringelement generating signals indicative of a volume of that receivedsolution, and C. a second pump, fluidly coupled to the mesne measuringelement, that routes PD solution from the mesne measuring element fordelivery to the patient.
 10. The apparatus of claim 11, wherein themesne measuring element generates the volume-indicating signals based ona height of received PD solution in the chamber.
 11. The apparatus ofclaim 9, wherein the mesne measuring element comprises one or moreilluminant sources that transmit one or more rays of illuminant throughthe chamber.
 12. The apparatus of claim 11, wherein one or more of therays transmitted by the illuminant source are coherent.
 13. Theapparatus of claim 11, wherein one or more of the rays transmitted bythe illuminant source are generated by laser light emitting diodes. 14.The apparatus of claim 9, wherein the mesne measuring element comprisingone or more image capture devices.
 15. The apparatus of claim 14,wherein the mesne measuring element generates the volume-indicativesignals as a function of a pattern of rays that are transmitted throughthe chamber and that are captured by the one or more image capturedevices.
 16. The apparatus of claim 15, comprising a processor thatcompares the pattern of rays captured by the one or more image capturedevices with one or more patterns generated during a calibration phase.17. The apparatus of claim 15, comprising a processor that compares thepattern of rays captured by the one or more image capture devices withone or more patterns generated when the chamber is empty of PD solution.18. An apparatus for delivering peritoneal dialysis (PD) solution from asupply to a patient, comprising A. a first pump, in fluid coupling withthe supply, that delivers PD solution from the supply to a mesnemeasuring element, the first pump generating first volume-indicatingsignals indicative of a volume of that delivered PD solution, B. themesne measuring element including a chamber that is in fluid couplingwith the first pump and that receives PD solution from the first pump,the mesne measuring element generating second volume-indicating signalsindicative of a volume of that received solution, and C. a peristalticpump, fluidly coupled to the mesne measuring element, that routes PDsolution from the mesne measuring element for delivery to the patient.19. The apparatus of claim 18, wherein the peristaltic pump pulls the PDsolution from the chamber of the mesne measuring element for delivery tothe patient.
 20. The apparatus of claim 1, wherein the peristaltic pumpdelivers the PD solution to the patient within a constant low-pressurerange.
 21. The apparatus of claim 16, wherein the low-pressure range isbetween 1.0 and 2.0 pounds-per-square-inch (psi).
 22. The apparatus ofclaim 18, wherein at least one of i. the first pump comprises a chamberthat is embodied in one or more cassettes, ii. the mesne measuringelement comprises a chamber that is embodied in said one or morecassettes, iii. the peristaltic pump comprises a fluid-flow pathembodied in said one or more cassettes.
 23. The apparatus of claim 18comprising a pressure detection element, fluidly and/or electricallycoupled to the second pump, that generates signals indicative of apressure at which the second pump routes the PD solution for delivery tothe patient.
 24. The apparatus of claim 20 comprising one or more fuzzylogic and/or processing elements to monitor and/or control operation ofthe first and second pumps.